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Naoki Yamauchi and Alley E. Watada

1 Prescnt address: Himeji College of Hyogo, Shinzaike-honcho, Himeji, Hyogo 670 Japan. 2 To whom reprint requests should be addressed. Paper no. W of the series “Mechanism of Chlorophyll Degradation in Harvested Leafy Vegetables”. We gratefully

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Yuji Yamada, Masayoshi Nakayama, Hiromitsu Shibata, Sanae Kishimoto and Takashi Ikeda

al., 2008 ). Thus, the change in purple color intensity that occurs in paprika fruit during development appears to be caused by changes in the anthocyanin contents, suggesting that both anthocyanin biosynthesis and degradation are involved in this

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K.A. Stewart, S. Jenni and K.A. Martin

In 1994, field trials were undertaken to evaluate the agronomic performance of a range of paper mulches in vegetable production. During the course of the experiments, the majority of the paper mulches tested degraded part way through the growing season. Before the next growing season, a range of Kraft papers differing in densities and compositions were subjected to an accelerated degradation test to determine which mulches would be suitable for use under Quebec field conditions. A mixture of equal parts black soil, sand, and manure (two parts sheep manure and one part liquid cow manure) was placed into trays of 26 x 52 cm. Experimental papers were cut into strips measuring 2.5 x l.5 cm and put into the trays such that half of the strips were covered with the mixture. The trays were placed in a growth cabinet (30C with a relative humidity of 50%). Three replicates of each treatment were sampled 3, 5, 7, 11, and 14 days after placement to determined the amount of degradation that had taken place. It was found that the length of time taken for degradation in the accelerated system was 3.7 times less than that of the field.

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Donald E. Irving, Glen J. Shingleton and Paul L. Hurst

Extractable activities of α-amylase, β-amylase, and starch phosphorylase were investigated in order to understand the mechanism of starch degradation in buttercup squash (Cucurbita maxima Duchesne ex Lam. `Delica') with the ultimate goal of improving the conversion of starch into sweet sugars. During rapid starch synthesis (0 to 30 days after flowering), extractable activities of α-amylase and β-amylase were low, but those of starch phosphorylase increased. After harvest, during ripening at 12 °C, or in fruit left in the field, activities of α-amylase and β-amylase increased. Starch contained 20% to 25% amylose soon after starch synthesis was initiated and until 49 days after harvest irrespective of whether the crop remained in the field or in storage at 12 °C. Maltose concentrations were low prior to harvest, but levels increased during fruit ripening. Data suggest starch breakdown is hydrolytic in buttercup squash, with α-amylase being the primary enzyme responsible for initiating starch breakdown.

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N. El-Assi, D.J. Huber and J.K. Brecht

The irradiation of harvested fruit is typically accompanied by excessive tissue softening, a process that is not well understood. In this study, we examined the role of specific cell wall polymers and the extent of general cell wall degradation and softening in irradiated tomato fruit. `Sunny' tomato fruit at mature-green and pink stages were subjected to X-ray radiation at 0, 83, and 156 Krad. Immediate softening was noted for both maturation classes, although some postirradiation recovery was evident in green fruit. Pectic polymers of both mature-green and pink fruit exhibited depolymerization and altered neutral sugar profiles in response to irradiation. Pectins, either as components of total ethanol-insoluble solids (EIS), purified by selective extraction, or of commercial origin were similarly affected by irradiation. Cellulose preparations were unaffected by irradiation. The data demonstrate that the effect of irradiation on the cell wall exhibits specificity, can occur nonenzymatically, and does not require initiating adducts of cytosolic origin.

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Graham H. Barry and Smit le Roux

studied extensively. Monselise et al. (1976) reported that paclobutrazol contributed to the acceleration of chlorophyll degradation of sweet orange. Gilfillan and Lowe (1985) demonstrated that paclobutrazol increased ‘Satsuma’ mandarin ( C. unshiu

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Jeremy S. Cowan, Debra A. Inglis and Carol A. Miles

growing interest in biodegradable plastics as an alternative to polyethylene for agricultural mulch. Biodegradable plastics are a class of plastic materials which degrade due to the action of naturally occurring microorganisms such as bacteria, fungi, and

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Henry G. Taber and D.F. Cox

Three trials, beginning June, July, and September 1991, examined the breakdown of photodegradable plastic bags. The plastic contained a light-sensitive compound dissolved in the polymer to hasten degradation. The bags were placed in east-west rows on bare ground. Other factors studied included turning the bags over either every 3 or 7 days and either filling the bags with fresh grass clippings or leaving them empty. Strength loss was determined with a hand-held puncture tester. Strength increased initially by 36%, 32%, and 63% in the three trials, respectively. The bags took 33, 35, and 64 days to reach brittleness (puncture strength of 180 g) in the three trials, respectively. Once degradation began, all trials showed similar rates of decline. However, the degradation began 7 days after exposure in the first two trials, but not until 14 days after exposure in the September trial. The addition of grass clippings to the bags increased the initial strength and delayed the onset of degradation. Turning the bags every 3 days rather than every 7 did not affect degradation.

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John M. Englert, Gary D. Coleman, Tony H.H. Chen and Leslie H. Fuchigami

A 32kDa bark storage protein (BSP) which accumulates in the fall and is degraded in the spring has been identified in Populus deltoides bark. The BSP gene has been shown to be regulated by short day (SD) photoperiod (8 h). The physiological condition of the plant and the environmental factors necessary for the degradation and retranslocation of BSP are of considerable interest for determining the role of this protein in the remobilization of nitrogen in trees.

Poplar plants were placed in a SD growth chamber for 4 or 7 weeks to induce growth cessation (bud set) or dormancy, respectively. BSP accumulated to high levels in bark tissues after 3 weeks SD and remained high through 7 weeks SD. Plants in which growth had stopped (4 weeks SD), or in which dormancy (7 weeks SD) was broken with hydrogen cyanamide (0.5 M) or chilling (4 weeks 0C) broke bud within 1 week of being placed into long day (LD) conditions. Dormant plants which were not chilled broke bud after 3 weeks LD. BSP levels decreased around the time of budbreak, suggesting that the degradation of BSP is dependent on the need for a nitrogen sink, ie. budbreak and new shoot growth.

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Naoki Yamauchi and Alley E. Watada

Pigments in stored parsley leaves (Petroselinum crispum Nym.) were monitored to determine if degradative products of chlorophyll (chl) differed while under different types of atmosphere. The leaves were stored in a closed container under a stream of humidified air at 20C with or without 10 ppm ethylene and with or without 10 percent oxygen and 10 percent carbon dioxide. Analysis of pigments with HPLC showed that chl a and b decreased sharply with or without ethylene and the decrease was considerably less under CA. Chlorophyll a-1, the oxidized form of chl a, was initially low, and the level decreased slightly with all of the storage conditions. Chlorophyllide was also low, but it increased slightly during storage. Xanthophyll derivatives, which appeared to be the esterified xanthophylls, increased slightly during storage. These results indicate that chl degradation in stored parsley leaves was hastened by ethylene or suppressed by CA condition and the pathway of chl degradation did not appear to be altered by the different storage atmospheres.